1. The anaerobic heat production of bull spermatozoa has been examined under varying environmental conditions, in an isothermal calorimeter, capacity 2·4 ml., working at atmospheric pressure. The minimum detectable heat production was 10
μ
cal/min. The calorimeter was calibrated with needles containing plutonium oxide of known heat production, both now and in the future. 2. Abnormal environmental conditions or treatments, such as washing, hypertonicity, hypotonicity and dilution elicited a shock reaction characterized by depressed metabolism, followed by a gradual recovery or adaptation, which in certain conditions was complete. 3. The effect of the pH of the suspending medium was examined under rigorous conditions. A low pH causes a reduction in metabolism but the response is not linear, there being a change in the relationship between heat production and pH within the range pH 6·9 to 6·4. The difference between the rate of heat production at pH 7·4 and 6·9 is insignificant, but at pH 6·4, heat production is reduced to nearly half its normal value. 4. The rate of heat production of bull spermatozoa in hypertonic and hypotonic media has been examined. The osmotic pressure range was from 3·4 to 15·1 atm, Δ = –0·28 to –1·25, or, in terms of mM-NaCl, 80 to 368. Hypertonic media in which Δ = –0·75, 0·22 below the normal tonicity, have a barely perceptible effect; but a hypotonic medium in which Δ = –0·42, 0·11 above the normal tonicity, has a depressant action, though adaptation occurs. 5. The depressant effect of hypertonicity and hypotonicity is less marked, relative to controls, at pH 6·4 than at 7·4. 6. The rate of anaerobic heat production declines before substrate exhaustion or a reduction in the pH of the medium are likely to have any effect on sperm metabolism. The following possible explanations are examined: (i) that the energy required for high sperm activity is of the same order as the rate of free energy change associated with anaerobic fructolysis; (ii) that the rate of
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. synthesis during anaerobic fructolysis does not keep pace with the rate of
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. hydrolysis necessary to provide the energy for high sperm activity.
Roles of miR-432 and circ_0000418 in mediating the anti-depressant action of ADAR1
